Mixed working fluid power system with incremental vapor generation

ABSTRACT

A power generating system ( 110 ) comprising a heat source ( 116 ) and an incremental vapor generator system ( 112 ) operatively associated with the heat source ( 116 ). The incremental vapor generator system ( 112 ) includes a first heating section ( 136 ) and a second heating section ( 138 ). The first heating section ( 136 ) receives a mixed working fluid ( 114 ) and generates a first heated working fluid stream comprising a vapor portion ( 120 ) and a liquid portion. The second heating section ( 138 ) is operatively associated with the first heating section ( 136 ) and receives the liquid portion from the first heated working fluid stream. The second heating section ( 138 ) generates a second heated working fluid stream comprising a vapor portion ( 122 ). An energy conversion device ( 126 ) operatively associated with the incremental vapor generator system ( 112 ) converts into useful work heat energy contained in the vapor portions ( 120, 122 ) of the first and second heated working fluid streams.

CONTRACTUAL ORIGIN OF THE INVENTION

[0001] The United States Government has rights in this inventionpursuant to Contract No. DEAC36-99GO10337 between the U.S. Department ofEnergy, and the National Renewable Energy Laboratory, a division of theMidwest Research Institute.

TECHNICAL FIELD

[0002] This invention relates to power generation systems in general andmore specifically to power generation systems utilizing mixed workingfluids.

BACKGROUND ART

[0003] Power generation systems or power plants are well-known in theart and are widely used to generate electricity. Most such powergeneration systems generate electricity from heat energy derived fromburning fossil fuels (e.g., coal or natural gas) and are referred toherein as thermal power plants. In addition to using heat energy derivedfrom burning fossil fuels, thermal power plants can also be used with awide variety of other heat sources, such as solar, geothermal, andnuclear sources.

[0004] Traditionally, thermal power plants have operated in accordancewith the well-known Rankine thermodynamic cycle. In the Rankine cycle, aso-called “pure” working fluid, such as water, is heated to producevapor or steam. The steam is then expanded, typically through a turbine,in order to convert heat energy contained therein into mechanical work.In the case of an electric power generation system, the turbine isoperatively connected to an electrical generator which produces theelectricity. While power plants operating in accordance with the Rankinecycle are well-known and widely used, certain characteristics of theRankine cycle impose fundamental limitations on the thermodynamicefficiency of the cycle. For example, a Rankine cycle operating with apure working fluid suffers some thermodynamic irreversibilities due tothe fact that the pure working fluid vaporizes at substantially constanttemperature. These irreversibilities can be larger or smaller dependingon the temperature difference between the heating medium and workingfluid.

[0005] Partly in an effort to solve some of the limitations associatedwith the use of a pure working fluid in the Rankine cycle, other typesof thermodynamic cycles (e.g., any of the so-called Kalina cycles) havebeen developed which utilize mixed working fluids. Briefly, a mixedcomponent working fluid comprises two or more vaporizable componentswhich vaporize and condense progressively over a temperature rangerather than at the relatively constant temperature of a so-called “pure”working fluid (e.g., water). Accordingly, thermodynamic cycles utilizingmixed working fluids can, if properly designed, realize increasedefficiencies over similar thermodynamic cycles (e.g., the Rankine cycle)that utilize pure working fluids, such as water.

[0006] One design consideration for mixed working fluid systems relatesto the boiler or vapor generator that is used to vaporize the mixedworking fluid. That is, since the mixed working fluid vaporizes over atemperature range, it is generally preferred to design the vaporgenerator so that heating function of the mixed working fluid closelyfollows the cooling function of the heating medium. Closely matching theheating and cooling functions of the working and heating fluids reducesthe thermodynamic irreversibilities during the heating cycle, thusincreasing the overall thermodynamic efficiency of the system. Inaccordance with this consideration, thermodynamic cycles utilizing mixedfluids often make use of countercurrent heat exchangers, in which theheating medium and mixed working fluid flow in opposite directions. Inthis manner, the heating function of the mixed working fluid can be madeto more closely follow the cooling function of the heating medium.

[0007] While such countercurrent heat exchangers have been used in mixedworking fluid systems to achieve some performance and efficiency gains,there is still room for improvement, particularly in light of otherrequirements or limitations of the particular type of power generationsystem in which the heat exchanger is to be used. For example, a primaryconsideration of geothermal power generation systems relates to theso-called “brine effectiveness,” that is, the amount of useful work thatcan be extracted or derived from a given brine flow rate. A desirablegeothermal power generation system will seek to maximize brineeffectiveness.

DISCLOSURE OF INVENTION

[0008] A power generating system according to the present invention maycomprise a heat source and an incremental vapor generator systemoperatively associated with the heat source. The incremental vaporgenerator system includes a first heating section and a second heatingsection. The first heating section receives a mixed working fluid andgenerates a first heated working fluid stream comprising a vapor portionand a liquid portion. The second heating section is operativelyassociated with the first heating section and receives the liquidportion from the first heated working fluid stream. The second heatingsection generates a second heated working fluid stream comprising avapor portion. An energy conversion device operatively associated withthe incremental vapor generator system converts into useful work heatenergy contained in the vapor portions of the first and second heatedworking fluid streams.

[0009] Also disclosed is a method for generating power from a mixedworking fluid that comprises the steps of incrementally heating themixed working fluid to produce a first vapor stream and a second vaporstream; and converting into useful work heat energy contained in thefirst and second vapor streams.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Illustrative and presently preferred embodiments of the inventionare shown in the accompanying drawings in which:

[0011]FIG. 1 is a schematic diagram of a power generating systemaccording to the present invention utilizing parallel flow incrementalvapor generation;

[0012]FIG. 2 is an equilibrium/phase diagram of the mixed working fluidat the various stations of the power generating system shown in FIG. 1;

[0013]FIG. 3 is a graphical representation of the heating and coolingfunctions of the mixed working fluid and the heating fluid for the powergenerating system shown in FIG. 1;

[0014]FIG. 4 is a schematic diagram of a second embodiment of a powergenerating system according to the present invention utilizing serialflow incremental vapor generation;

[0015]FIG. 5 is an equilibrium/phase diagram of the mixed working fluidat the various stations of the power generating system shown in FIG. 4;and

[0016]FIG. 6 is a graphical representation of the heating and coolingfunctions of the mixed working fluid and the heating fluid for the powergenerating system of FIG. 4.

BEST MODES FOR CARRYING OUT THE INVENTION

[0017] A power generating system 110 according to one embodiment of thepresent invention is shown in FIG. 1 and may comprise an incrementalvapor generator system 112 for vaporizing a mixed working fluid 114. Theincremental vapor generator system 112 incrementally vaporizes the mixedworking fluid 114 with heat energy extracted from a heat source, suchas, for example, geothermal brine 116. Alternatively, and as will bedescribed in greater detail below, the present invention may be utilizedwith other types of heat sources and/or other types of heating fluids.

[0018] In the embodiment shown in FIG. 1, the incremental vaporgenerator system 112 comprises a parallel flow incremental vaporgeneration system 118 in which the mixed working fluid 114 isincrementally vaporized to form a first vapor portion 120 and a secondvapor portion 122. The first and second vapor portions 120 and 122thereafter may be combined in a vapor mixer 124 before being directed toan energy conversion system 126, which converts energy contained in thefirst and second vapor portions 120 and 122 into useful work heat. Inthe embodiment shown in FIG. 1, energy conversion system 126 comprises aturbine 128 and an electrical generator 130. Accordingly, heat energycontained in the first and second vapor portions 120, 122 is convertedinto electrical energy by the energy conversion system 126. In analternate embodiment described below, the incremental vapor generatorsystem may comprise a series flow incremental vapor generation system218 (FIG. 4) in which the mixed working fluid is incrementally vaporizedin a serial manner.

[0019] The parallel flow incremental vapor generating system 118utilized in the first embodiment 110 of the power generating systemaccording to the present invention is shown in FIG. 1 and may comprise aheat exchanger or vaporizer 132 having a primary loop 134 through whichis caused to flow the heating fluid, e.g., geothermal brine 116. Theheat exchanger or vaporizer 132 may also comprise first and secondheating sections 136 and 138 that are in thermal communication with theprimary loop 134 so that heat energy contained in the heating fluid(e.g., brine 116) is transferred to the mixed working fluid 114 flowingthrough the first and second heating sections 136 and 138, respectively.The heat exchanger 132 may also be provided with a third heating section140 suitable for additionally heating the first and second vaporportions 120 and 122 in a manner that will be described in more detailbelow.

[0020] The first and second heating sections 136 and 138 are operativelyassociated with respective first and second separator systems 142 and144. The first and second separator systems 142 and 144 separate liquidand vapor portions from the heated mixed working fluid introducedtherein by the first and second heating sections 136 and 138,respectively. More specifically, a first inlet 146 of the firstseparator 142 is connected to the outlet 148 of the first heatingsection 136, whereas a liquid outlet 150 of the first separator 142 isconnected to the inlet 152 of the second heating section 138. A secondinlet 154 of first separator 142 is connected to a high temperaturerecuperator 156. A vapor outlet 158 of first separator 142 is connectedto the vapor mixer 124.

[0021] The second separator 144 is provided with an inlet 160 that isconnected to the outlet 162 of the second heating section 138. A liquidoutlet 164 of second separator 144 is connected to the high temperaturerecuperator 156, whereas a vapor outlet 166 is connected to the vapormixer 124.

[0022] The vapor mixer 124 is provided with a vapor outlet 168 which, inthe embodiment shown and described herein, is connected to the thirdheating section 140. The third heating section 140 is used to furtherheat (e.g., superheat) the vaporized mixed working fluid 114 exiting themixer 124. The outlet 170 of the third heating section 140 is connectedto the energy conversion system 126. As mentioned above, the energyconversion system 126 may comprise a turbine 128 and electricalgenerator 130. The exhaust outlet 172 of turbine 128 is connected to alow temperature recuperator 174. The low temperature recuperator 174 isin turn connected to a condenser 176 via a mixer 178. The condenser 176is operatively connected to the heat exchanger 132 via a pump 180 andthe high and low temperature recuperators 156 and 174, respectively.

[0023] The power generation system 110 may be operated as follows toconvert into useful work heat energy contained in the heating fluid(e.g., geothermal brine 116). As was briefly described above, the mixedworking fluid 114 utilized herein vaporizes progressively over anincreasing temperature range. That is, the temperature of the vapor andliquid comprising the heated mixed working fluid 114 increases withincreasing quality. The point at which vaporization begins (i.e., at 0%quality) is referred to herein as the “bubble point,” whereas the pointat which vaporization is complete (i.e., at 100% quality) is referred toherein as the “dew point.” By way of example, the mixed working fluid114 utilized in the preferred embodiments shown and described hereincomprises a mixture of ammonia and water. Alternatively, other mixedworking fluids could be used as well.

[0024] Referring now to FIGS. 1 and 2 simultaneously, the mixed workingfluid feed stream 114 exits the condenser 176 at about the bubble pointfor the mixture. This corresponds to station L₀ in FIG. 1 and thecorresponding point L₀ in FIG. 2. Before proceeding with thedescription, it should be noted that various points in the system 110that are of interest thermodynamically are referred to herein as“stations” and are indicated in FIGS. 1 and 4 as encircled numbers orencircled letter-number combinations. Such stations are indicated on theequilibrium/phase diagrams (e.g., FIGS. 2 and 5) as points havingcorresponding numbers or letter-number combinations. Hence, station L₀is designated in FIG. 1 as encircled legend “L₀”. The correspondingpoint in the equilibrium/phase diagram illustrated in FIG. 2 is alsodesignated “L₀”.

[0025] Continuing now with the description, the pump 180 increases thepressure of the mixed working fluid 114 to a point suitable for use inthe high pressure side of the power generation system 110. The flow ofthe working fluid 114 is then split, with a first stream 182 beingdirected through the high temperature recuperator 156 and a secondstream 184 being directed to the low temperature recuperator 174. Theheating characteristics of the high temperature recuperator 156 and theflow rate of the first stream 182 are selected so that the first stream182 is heated to a point above its bubble point at the particularpressure involved (e.g., about 425 pounds per square inch absolute(psia)). That is, the first stream 182 is heated to a quality greaterthan zero. By way of example, in one preferred embodiment, the firststream 182 is heated to a quality in the range of about 10% to about 40%(30% preferred). This quality corresponds to a vapor portion in therange of about 80% to about 96% (90% preferred) on a volume basis. Theheated first stream 182 is then directed to the inlet 154 of firstseparator system 142. This is identified as station 2 ₁ in FIG. 1 and aspoint 2 ₁ in FIG. 2.

[0026] The second stream 184 is heated by the low temperaturerecuperator 174 and thereafter is directed to the first heating section136 of heat exchanger 132 where it is additionally heated to atemperature that exceeds the bubble point. This corresponds to station 2₃ in FIG. 1 and to point 2 ₃ in FIG. 2. It is generally preferred thatthe heating characteristics of the low temperature recuperator 174 andthe first heating section 136, as well as the flow rate of the secondstream 184 be such that the mixed working fluid 114 comprising thesecond stream 184 is heated to about the same quality as the firststream 182. That is, it is preferred that the points 2 ₁ and 2 ₃ on FIG.2 be approximately coincident. The heated second stream 148 from thefirst heating section 136 is then directed to the first inlet 146 of thefirst separator 142.

[0027] The first separator system 142 receives the first and secondheated streams 182 and 184 and separates the two streams 182 and 184into a liquid portion and a vapor portion. The liquid portion exits theliquid outlet 150 of the separator 142 and is directed to the inlet 152of the second heating section 138. The vapor portion exits the vaporoutlet 158 of the first separator 142 as first vapor stream 120. Thefirst vapor stream 120 is at about the dew point (i.e., 100% quality)for the particular concentration of the mixed working fluid 114comprising the vapor portion stream 120. This corresponds to station v₁in FIG. 1 and to point v₁ in FIG. 2.

[0028] Before proceeding with the description it should be noted thatthe concentrations of the constituents (e.g., ammonia and water)comprising the mixed working fluid 114 are different for the liquid andvapor portions. For example, with reference now to FIG. 2, in onepreferred embodiment wherein the mixed working fluid 114 comprises amixture of ammonia and water, the first vapor portion stream 120(corresponding to point v₁ in FIG. 2) of the mixed working fluid 114comprises a higher concentration of ammonia (e.g., slightly greater thanabout 0.95 on a mass basis) than does the liquid portion (point 3 inFIG. 2) of the mixed working fluid 114. The liquid portion of the mixedworking fluid 114 at point 3 has an ammonia concentration that isslightly less than about 0.55 (on a mass basis). Consequently, anycharacteristics (e.g., quality) specifically recited herein for themixed working fluid 114 at a particular station refer to the workingfluid 114 in the particular state (e.g., vapor or liquid) and at thecorresponding concentration at the referenced station. For example, atstation v₁, the mixed working fluid 114 comprises a vapor having anammonia concentration that is slightly greater than about 0.95 and is atabout the dew point (i.e., a quality of about 100%) for the mixture atthat particular ammonia concentration. At station 3, the mixed workingfluid 114 comprises a liquid having an ammonia concentration that isslightly less than about 0.55 and is at about the bubble point (i.e., aquality of about 0%) for the mixture at the lower ammonia concentration.The ammonia concentrations (i.e., mass fractions) for the ammonia/watermixed working fluid 114 that may be utilized in the preferredembodiments of the present invention are shown in FIGS. 2 and 4 for thecorresponding liquid and vapor portions of the mixed working fluid atthe various stations.

[0029] With the foregoing points in mind, the liquid portion of themixed working fluid 114 from the first separator 142 is at about thebubble point of the liquid portion of mixed working fluid 114 at thecorresponding ammonia concentration. That is, the liquid portion is atabout the bubble point for the lower ammonia concentration of the liquidportion of the mixed working fluid 114. This corresponds to station 3 inFIG. 1 and to point 3 in FIG. 2. The liquid portion is directed into theinlet 152 of the second heating section 138 whereupon it is heated to atemperature in excess of the bubble point. It is generally preferredthat the liquid portion be heated in the second heating section 138 toabout the same quality as the mixed working fluid at stations 2 ₁ and 2₃. That is, the quality of the mixed working fluid stream exiting thesecond heating section 138 should be about the same as the qualities ofthe working fluid streams exiting the first heating section 136 and thehigh temperature recuperator 156. For example, in the embodiment shownand described herein, the mixed working fluid stream exits the secondheating section 138 at a quality in the range of about 10% to about 40%(30% preferred), which corresponds to a vapor portion in the range ofabout 80% to about 96% (90% preferred) on a volume basis. Thiscorresponds to station 4 in FIG. 1 and to point 4 in FIG. 2.

[0030] The second separator system 144 receives the heated mixed fluidfrom the second heating section 138 and separates the heated mixed fluidinto a liquid portion and a vapor portion. The liquid portion exits theliquid outlet 164 of the separator 144 and is directed to the hightemperature recuperator 156 whereupon it surrenders a portion of itsheat to the first working stream 182. The vapor portion from separator144 exits the vapor outlet 166 as the second vapor portion stream 122.The second vapor portion stream 122 is at about the dew point (i.e.,100% quality) for the higher ammonia concentration of the mixed workingfluid 114 that comprises the second vapor portion stream 122. Seestation v₂ in FIG. 1 and point v₂ in FIG. 2.

[0031] The vapor mixer 124 receives the first and second vapor streams120 and 122 and combines them into a combined vapor stream 186. Thecombined vapor stream 186 corresponds to station v₃ in FIG. 1 and topoint v₃ in FIG. 2. The combined vapor stream 186 may be additionallyheated (e.g., superheated) by the third heating section 140 to atemperature greater than the dew point temperature for the combinedvapor stream 186. The superheated stream 188 exiting the third heatingsection 140 corresponds to station v₄ in FIG. 1 and to point v₄ in FIG.2. The stream 188 is then directed to the energy conversion system 126.

[0032] The energy conversion system 126 extracts heat energy from thesuperheated stream 188, converting it into useful work. In theembodiment shown and described herein, heat energy contained in thefirst and second vapor streams 120 and 122 (which comprise combinedstream 186 and superheated stream 188) is converted into electrical workby the turbine 128 and the electrical generator 130 comprising theenergy conversion system 126.

[0033] The exhaust stream 172 from the turbine 128 corresponds tostation v₅ in FIG. 1 and to point v₅ in FIG. 2 and is at a temperaturethat is greater than the dew point temperature for the mixed workingfluid at the reduced pressure on the low pressure side of the powergenerating system 110. By way of example, in the embodiment shown anddescribed herein, the mixed working fluid 114 is at a pressure of about71 psia on the low pressure side. Alternatively, the exhaust streamcould exit the turbine 128 at a temperature below the dew point of themixed working fluid if the turbine is capable of handling wet mixtures.The exhaust stream 172 from turbine 128 is thereafter directed to thelow temperature recuperator 174 wherein it surrenders a portion of itsheat energy to the second working fluid stream 184. The cooled exhauststream 172 exits the low temperature recuperator 174 at station v₆ at atemperature between the bubble and dew points for the mixed workingfluid. By way of example, in one preferred embodiment, the cooledexhaust stream 172 exits the low temperature recuperator 174 at aquality in the range of about 0% to about 100% (45% preferred). See alsopoint v₆ in FIG. 2.

[0034] The mixed working fluid exiting the low temperature recuperator174 is then mixed with the liquid portion exiting the high temperaturerecuperator 156 in the mixer 178. The combined working fluid streamexits mixer 178 at station v₇ which corresponds to point v₇ in FIG. 2.The combined working fluid stream is then condensed to the bubble point(station L₀ in FIG. 1 and point L₀ in FIG. 2) by the condenser 176. Thecondensed stream is then returned to the high pressure side of thesystem by pump 180 and the cycle is repeated.

[0035] A significant advantage of the power generating system 110according to the present invention is that it results in closely matchedheating and cooling curves for the working and heating fluids,respectively. For example, with reference now to FIG. 3 the heatingcurve or function 190 of the mixed working fluid closely follows thecooling curve or function 192 of the heating fluid (e.g., brine 116).The closely matched heating and cooling functions 190 and 192, improvesthermodynamic efficiency by reducing the irreversibilities occurring inthe heat exchanger 132. The closely matched heating and coolingfunctions also allow the brine 116 to be cooled to a lower temperature,closer to the bubble point of the working fluid, than is possible withprior systems. Consequently, the power generating system 110 of thepresent invention substantially reduces the heating fluid (e.g., brine116) flow rate required for a given amount of useful work. Accordingly,the power generating system 110 can be used with considerable advantagein geothermal power generation systems wherein it is desired to minimizethe brine flow rate per kilowatt of electricity produced.

[0036] Having briefly described one embodiment of the power generatingsystem 110, as well as some of its more significant features andadvantages, the various embodiments of the power generating systemaccording to the present invention will now be described in detail.However, before proceeding with the description, it should be noted thatwhile the various embodiments of the power generating system are shownand described herein as they could be used in a geothermal electricalgenerating system utilizing hot brine 116 as the heating fluid, thepresent invention is not limited to use in geothermal electricalgenerating systems. In fact, power generating systems according to thepresent invention could be used with any of a wide variety of heatingfluids and working fluids that are now known in the art or that may bedeveloped in the future, as would be obvious to persons having ordinaryskill in the art after having become familiar with the teachings of thepresent invention. Consequently, the present invention should not beregarded as limited to the particular applications and/or heating andworking fluids shown and described herein.

[0037] With the foregoing considerations in mind, one embodiment of apower generating system 110 according to the present invention comprisesan incremental vapor generator system 112 for vaporizing a mixed workingfluid 114 utilizing heat obtained from a suitable heat source. By way ofexample, in the embodiments shown and described herein, the heat sourcemay comprise geothermal brine 116. The geothermal brine 116 comprisesthe heat source or heating fluid and is used to vaporize the workingfluid 114 in the incremental vapor generator system 112.

[0038] The working fluid 114 used in the power generation system 110 maycomprise any of a wide range of mixed, non-azeotropic fluids now knownin the art or that may be developed in the future suitable for use inthe particular application. As used herein, the term “mixed fluid”refers to any fluid wherein the temperature of the vapor and liquidcomponents increases with increasing quality. By way of example, in theembodiment shown and described herein, the mixed working fluid comprisesa mixture of ammonia and water.

[0039] As was briefly mentioned above, in one embodiment of theinvention the incremental vapor generator system 112 comprises aparallel flow incremental vapor generation system 118. In the parallelflow incremental vapor generation system 118, the mixed working. fluid114 is incrementally vaporized to form a first vapor portion 120 and asecond vapor portion 122. The first and second vapor portions 120 and122 are combined (i.e., in a parallel manner) before being directed tothe energy conversion system 126, hence the designation parallel flowincremental vapor generation system 118.

[0040] With reference now primarily to FIG. 1, the parallel flowincremental vapor generating system 118 utilized in one embodiment ofthe power generating system 110 according to the present inventioncomprises a heat exchanger or vaporizer 132 having a primary loop 134through which is caused to flow the heating fluid. As mentioned above,in the embodiment shown and described herein, the heating fluidcomprises geothermal brine 116. Alternatively, other types of heatingfluids may be used, as would be obvious to persons having ordinary skillin the art after having become familiar with the teachings of thepresent invention.

[0041] The heat exchanger or vaporizer 132 may also comprise first andsecond heating sections 136 and 138 arranged so that they are in thermalcommunication with the primary loop 134. Accordingly, heat energycontained in the brine 116 is transferred to the mixed working fluid 114flowing in the first and second heating sections 136 and 138,respectively. The heat exchanger 132 may also be provided with a thirdheating section 140 suitable for additionally heating the first andsecond vapor portions 120 and 122. For example, in the embodiment shownand described herein, the third heating section 140 is used to heat thefirst and second vapor portions 120 and 122 above the dew point, aprocess that is commonly known as “superheating.”

[0042] It is generally preferred that the heat exchanger 132 comprise acounter-current heat exchanger in which the inlet end of the primaryloop 134 is thermally adjacent the “hottest” heating section (e.g., thethird heating section 140) and in which the outlet end is thermallyadjacent the “coolest” heating section (e.g, the first heating section136). Such an arrangement makes it easier to more closely match theheating function 190 of the working fluid 114 with the cooling function192 of the heating fluid (e.g., brine 116). See FIG. 3.

[0043] The exact number of heating sections (e.g., heating sections 136,138, and 140) comprising the heat exchanger 132 may vary depending onthe particular application, the particular heating and working fluidsused, as well as on the number of stages (e.g., vapor separators) usedto achieve the incremental heating of the working fluid in the mannershown and described herein. That is, the number of heating sectionscomprising the heat exchanger in any given application could be readilydetermined by persons having ordinary skill in the art after havingbecome familiar with the teachings of the present invention and byapplying the teachings to the particular application. Consequently, thepresent invention should not be regarded as limited to a heat exchangerhaving any particular number of heating sections.

[0044] The heat exchanger 132 may be constructed from any of a widerange of materials and in accordance with any of a wide range oftechniques that are now known in the art or that may be developed in thefuture that would be suitable for the particular application. However,since heat exchangers of the type described herein could be readilyfabricated by persons having ordinary skill in the art after havingbecome familiar with the teachings of the present invention, and sincethe details of such heat exchangers are not necessary to understand orpractice the present invention, the heat exchangers used in theembodiments shown and described herein will not be described in furtherdetail herein.

[0045] The first and second heating sections 136 and 138 of the heatexchanger 132 are operatively associated with first and second separatorsystems 142 and 144. As will be described in greater detail below, thefirst and second separator systems 142 and 144 separate liquid and vaporportions (not shown) from the heated mixed working fluid introducedtherein by the first and second heating sections 136 and 138,respectively.

[0046] The first separator system 142 comprises a first inlet 146, asecond inlet 154, a liquid outlet 150, and a vapor outlet 158. The firstinlet 146 is connected to the outlet 148 of the first heating section136 so that heated mixed working fluid from the first heating section136 enters the separator system 142. The second inlet 154 of the firstseparator system 142 is connected to the high temperature recuperator156 so that the first mixed working fluid stream 182 from the hightemperature recuperator 156 is also directed into the separator system142. The liquid outlet 150 of the first separator system 142 isconnected to the inlet 152 of the second heating section 138 of heatexchanger 132. The vapor outlet 158 of the first separator system 142 isconnected to the vapor mixer 124.

[0047] The first separator system 142 may comprise any of a wide rangeof separator systems that are well-known in the art that would besuitable for separating vapor and liquid portions from an incoming wetmixture stream (e.g., the heated working fluid 114). Consequently, thepresent invention should not be regarded as limited to any particulartype of separator system.

[0048] The second separator system 144 may be similar to the firstseparator system 142, except that the second separator system 144 isprovided with but a single inlet 160 connected to the outlet 162 of thesecond heating section 138. The arrangement is such that the secondseparator system 144 receives the heated mixed working fluid 114 fromthe second heating section 138 of heat exchanger 132. A liquid outlet164 of the second separator 144 is connected to the high temperaturerecuperator 156, whereas a vapor outlet 166 is connected to the vapormixer 124.

[0049] The high temperature recuperator 156 connected to the liquidoutlet 164 of second separator system 144 is used to recover heatcontained in the liquid portion separated by the second separator 144.The recovered heat is used to pre-heat the first mixed working fluidstream 182. In the embodiment shown and described herein, the liquidoutlet 164 of the second separator 144 is connected to a heating loop155 of the high temperature recuperator 156, whereas a heated loop 157of high temperature recuperator 156 is connected between the pump 180and the second inlet 154 of first separator system 142. The separatedliquid portion in the heating loop surrenders heat to the first mixedworking fluid stream 182 in the heated loop 157, thereby pre-heating thefirst mixed working fluid stream 182. Thereafter, the separated liquidportion passes through an expansion valve 194 before entering the lowpressure side of the system 110.

[0050] The vapor mixer 124 is connected to the vapor outlets 158 and 166of the respective first and second separator systems 142 and 144 andreceives the corresponding first and second vapor portions 120 and 122.A vapor outlet 168 on the mixer 124 is connected to the third heatingsection 140. The outlet 170 of the third heating section 140 isconnected to the energy conversion system 126.

[0051] The vapor mixer 124 may comprise any of a wide range of devicesknown in the art or that may be developed in the future that would besuitable for mixing together the first and second vapor portions 120 and122. Consequently, the present invention should not be regarded aslimited to any particular type of vapor mixer system.

[0052] The energy conversion system 126 may comprise any of a wide rangeof systems and devices suitable for converting into useful work heatenergy contained in the heated mixed working fluid 114 exiting theparallel flow vapor generator 118 (or third heating section 140, if athird heating section is used). By way of example, in the embodimentsshown and described herein, the energy conversion system 126 comprises aturbine 128 and an electric generator 130 connected thereto. The turbine128 and electric generator 130 may comprise any of a wide range ofsystems and devices that are well-known in the art and readilycommercially available. Consequently, the turbine 128 and electricgenerator 130 utilized in one preferred embodiment of the invention willnot be described in greater detail herein.

[0053] The exhaust outlet 172 of turbine 128 is connected to a lowtemperature recuperator 174. The low temperature recuperator 174recovers heat contained in the turbine exhaust stream and uses it topre-heat the second mixed working fluid stream 184. More specifically,the exhaust outlet 172 of turbine 128 is connected to a heating loop 173of the low temperature recuperator 174, whereas a heated loop 175 of thelow temperature recuperator 174 is connected between the pump 180 andthe first heating section 136 of the heat exchanger 132. The turbineexhaust stream in the heating loop 173 surrenders heat to the secondmixed working fluid stream 184 in the heated loop 175, therebypre-heating the second mixed working fluid stream 184 before the sameenters the first heating section 136. Thereafter, the exhaust stream iscombined in the mixer 178 with the separated liquid portion exiting theexpansion valve 194. A condenser 176 connected to the mixer 178 receivesthe combined cooled mixed working fluid 114, condenses it, and returnsit to pump 180.

[0054] The condenser 176 may comprise any of a wide range of condensersthat are well-known in the art or that may be developed in the futurethat would be suitable for condensing the combined cooled mixed workingfluid 114 from the mixer 178. By way of example, in the embodiment shownand described herein, the condenser 176 comprises an air-cooledcondenser in which air 196 is used to condense the mixed working fluid114 flowing in the condenser 176. Alternatively, other cooling mediabesides air may be used to condense the mixed working fluid 114.

[0055] The power generation system 110 may be operated as follows toconvert into useful work heat energy derived from the heating fluid.Consider, for example, a geothermal power generation system whichgenerates electricity from geothermal brine 116 extracted from theearth. The geothermal brine 116 serves as the heating fluid and, in theexample described herein, enters the primary loop 134 of the heatexchanger 132 at a temperature of about 335° F., although othertemperatures are possible. The mixed working fluid 114 may comprise amixture of ammonia and water and is maintained at a pressure of about425 pounds per square inch absolute (psia) on the high pressure side ofthe power generating system 110. The low pressure side of the powergenerating system 110 is maintained at a pressure of about 71 psia.Alternatively, other mixed fluids may be used at other pressures, aswould be obvious to persons having ordinary skill in the art afterhaving become familiar with the teachings of the present invention. Theammonia/water mixture that comprises the mixed working fluid 114vaporizes progressively over an increasing temperature range. That is,the temperature of the vapor and liquid comprising the heated mixedworking fluid increases with increasing quality.

[0056] Referring now to FIGS. 1-3, the mixed working fluid feed stream114 exits the condenser 176 at station L₀ at about the bubble point forthe mixture 114. This station corresponds to point L₀ in FIG. 2. Thepump 180 increases the pressure of the mixed working fluid 114 to apressure suitable for use in the high pressure side of the powergenerating system 110. In the embodiment shown and described herein, thehigh pressure side of the system 110 is maintained at a pressure ofabout 425 psia. Therefore, the pump 180 increases the pressure of themixed working fluid 114 to a pressure of about 425 psia. The mixedworking fluid stream 114 exiting the pump 180 is then split into a firstworking fluid stream 182 and a second working fluid stream 184. Thefirst working fluid stream 182 is directed through the heated loop 157of the high temperature recuperator 156 whereupon it is heated by theliquid portion from the second separator 144 passing through the heatingloop 155. The heating characteristics of the high temperaturerecuperator 156 and the flow rate of the first stream 182 are such thatthe first stream 182 is heated to a temperature in excess of its bubblepoint. This corresponds to station 2 ₁ in FIG. 1 and to point 2 ₁ inFIG. 2.

[0057] By way of example, in the embodiment shown and described herein,the first stream 182 is heated to a quality in the range of about 10% toabout 40% (30% preferred). This quality range corresponds to a vaporportion range of about 80% to about 96% (90% preferred) on a volumebasis. So heating the first working fluid stream 182 to a vapor portionin the range specified herein provides for good heat transfercharacteristics in the high temperature recuperator 156. That is, someloss of efficiency in the high temperature recuperator 156 will occur ifthe first working fluid stream 182 is heated to a vapor portion that issubstantially greater than the vapor portion range specified herein.After being heated in the high temperature recuperator 156, the heatedfirst working fluid stream 182 is directed to the inlet 154 of the firstseparator system 142.

[0058] The second working fluid stream 184 is directed to the heatedloop 175 of the low temperature recuperator 174 whereupon it ispre-heated by the exhaust stream 172 exiting the turbine 128.Thereafter, the pre-heated second working fluid stream 184 is directedto the first heating section 136 of heat exchanger 132 which heats thesecond working fluid stream 184 to a temperature in excess of the bubblepoint. This corresponds to station 2 ₃ in FIG. 1 and to point 2 ₃ inFIG. 2. It is generally preferred that the flow rate of the secondstream 184 be matched to the heating characteristics of the lowtemperature recuperator 174 and the first heating section 136 so thatthe mixed working fluid 114 comprising the second working fluid stream184 is heated to about the same quality as the first stream 182. Thatis, it is preferred that the points 2 ₁ and 2 ₃ in FIG. 2 beapproximately coincident. Stated another way, the second working fluidstream 184 is heated to a quality in the range of about 10% to about 40%(30% preferred), which corresponds to a vapor portion in the range ofabout 80% to about 96% (90% preferred).

[0059] In the embodiment shown and described herein, the mass ratio ofthe first working fluid stream 182 to the second working fluid stream184 is about 1:4. That is, most of the working fluid 114 is directed tothe second stream 184, with only a small amount (i.e., ¼ on a massbasis) being directed through the high temperature recuperator 156 asfirst working fluid stream 182. Of course, the mixed working fluidstream 114 may be divided in accordance with other mass ratios dependingon the characteristics of the particular system.

[0060] Referring back now primarily to FIG. 1, the first separatorsystem 142 receives the first and second heated streams 182 and 184 andseparates the two streams 182 and 184 into a liquid portion and a vaporportion. The liquid portion exits the liquid outlet 150 of the firstseparator 142 and is directed to the inlet 152 of the second heatingsection 138. The vapor portion exits the vapor outlet 158 of the firstseparator 142 as a first vapor portion stream 120. The first vaporportion stream is at about the dew point (i.e., 100% quality) for themixed working fluid 114. This corresponds to station v₁ in FIG. 1 and topoint v₁ in FIG. 2.

[0061] The liquid portion from the first separator 142 is at about thebubble point of the mixed working fluid 114. See station 3 in FIG. 1 andpoint 3 in FIG. 2. The liquid portion is directed into the inlet 152 ofthe second heating section 138 whereupon it is heated to a temperaturein excess of the bubble point. It is generally preferred that the liquidportion be heated to about the same quality as the mixed working fluidat stations 2 ₁ and 2 ₃. That is, the quality of the mixed working fluidstream exiting the second heating section 138 should be about the sameas the qualities of the working fluid streams exiting the first heatingsection 136 and the high temperature recuperator 156. For example, inthe embodiment shown and described herein, the mixed working fluidstream exits the second heating section 138 at a quality in the range ofabout 10% to about 40% (30% preferred). This corresponds to a vaporportion in the range of about 80% to about 96% (90% preferred). Seestation 4 in FIG. 1 and point 4 in FIG. 2. As discussed above, heatingthe mixed working fluid to the quality ranges specified herein providesa good balance between temperature rise and heat transfer efficiency inthe second heating section 138.

[0062] The second separator system 144 receives the heated mixed fluidfrom the second heating section 138 and separates the heated mixed fluidinto a liquid portion and a vapor portion. The liquid portion exits theliquid outlet 164 of the separator 144 and is directed to the hightemperature recuperator 156 whereupon it surrenders a portion of itsheat to the first working fluid stream 182. Thereafter, the cooledliquid portion is expanded through the expansion valve 194 to the lowpressure side of the power generating system 110. See station 5 ₂ inFIG. 1 and point 5 ₂ in FIG. 2. The cooled, expanded liquid portion isthen combined with the turbine exhaust stream in mixer 178.

[0063] The vapor portion from the second separator 144 exits the vaporoutlet 166 of separator 144 as the second vapor portion stream 122. Thesecond vapor portion stream 122 is at about the dew point (i.e., 100%quality) and corresponds to station v₂ in FIG. 1 and to point v₂ in FIG.2.

[0064] The vapor mixer 124 receives the first and second vapor streams120 and 122 and combines them into a combined vapor stream 186. Thecombined vapor stream 186 corresponds to station v₃ in FIG. 1 and topoint v₃ in FIG. 2. If desired, the combined vapor stream 186 may beadditionally heated by the third heating section 140 to a temperaturegreater than the dew point temperature for the combined vapor stream186. That is, the combined vapor stream 186 may be superheated in thethird heating section 140. The superheated stream 188 exiting the thirdheating section 140 is designated as station v₄ in FIG. 1 andcorresponds to point v₄ in FIG. 2. The stream 188 is then directed tothe energy conversion system 126.

[0065] The energy conversion system 126 extracts heat energy from thesuperheated stream 188, converting it into useful work. In theembodiment shown and described herein, heat energy contained in thefirst and second vapor streams 120 and 122 (which comprise combinedstream 186 and superheated stream 188) is converted into electrical workby the turbine 128 and the electrical generator 130 comprising theenergy conversion system 126.

[0066] The superheated stream 188 is expanded in the turbine 128 andexits the turbine 128 as exhaust stream 172. See station v₅ in FIG. 1and point v₅ in FIG. 2. It is generally preferred that the expansionprocess be terminated before the mixed working fluid 114 is cooled belowthe dew point temperature. By way of example, in the embodiment shownand described herein, the mixed working fluid 114 is expanded to apressure of about 71 psia and to a temperature of about 150° F., whichis below the dew point. That is, the mixed working fluid 114 is cooledto a temperature below the dew point temperature since, in theembodiment shown and described herein, the energy conversion device 126functions effectively with wet mixtures. The exhaust stream 172 isthereafter directed to the low temperature recuperator 174 wherein itsurrenders a portion of its heat energy to the second working fluidstream 184 flowing in the heated loop 175 of low temperature recuperator174. The cooled exhaust stream 172 exits the low temperature recuperator174 at station v₆ at a temperature between the bubble and dew points forthe mixed working fluid. See point v₆ in FIG. 2. By way of example, inthe embodiment shown and described herein, the cooled exhaust stream 172exits the low temperature recuperator 174 at a quality in the range ofabout 0% to about 100% (45% preferred).

[0067] The mixed working fluid exiting the low temperature recuperator174 is then mixed in mixer 178 with the liquid portion flowing throughthe expansion valve 194. The combined working fluid stream that exitsmixer 178 is designated as station v₇ and corresponds to point v₇ inFIG. 2. The combined working fluid stream is then condensed by thecondenser 176 to about the bubble point, (i.e., at station L₀ in FIG. 1and point L₀ in FIG. 2). The condensed stream is then returned to thehigh pressure side of the system by pump 180 and the cycle is repeated.

[0068] The power generating system 110 just described results in theclosely matched heating and cooling functions 190 and 192 shown in FIG.3. That is, the heating curve 190 of the mixed working fluid 114 closelyfollows the cooling curve 192 of the heating fluid (e.g., geothermalbrine 116).

[0069] As mentioned above, the first embodiment 110 of the powergenerating system according to the present invention utilizes a parallelflow vapor generator system 118 in which the working fluid isincrementally vaporized to produce first and second vapor portionstreams 120 and 122 which are then combined in a parallel manner (e.g.,by mixer 124) before being superheated (if desired) and directed to theenergy conversion system 126. However, other incremental vaporizationarrangements are possible in accordance with the teachings of thepresent invention.

[0070] With reference now to FIGS. 4-6, a second embodiment 210 of apower generating system according to the present invention embodies anincremental vapor generator system 212 that comprises a series flowvapor generator system 218. Briefly, in the series flow vapor generatorsystem 218, the mixed working fluid 214 is incrementally vaporized toform a first vapor portion 220 and a second vapor portion 222. The firstvapor portion 220 is then used to condense or separate a liquid portionfrom a heated mixed working fluid stream 221 from which is derived thesecond vapor portion 222. Since, in the case of the mixed working fluid214, the liquid is “lean” and the first vapor portion 220 is “rich,” thefirst vapor portion 220 condenses on the lean liquid. The heat ofcondensation causes additional vapor to be produced. Accordingly, theseries flow vapor generator system 218 produces the vapor streams 220and 222 in a serial manner.

[0071] With reference now primarily to FIG. 4, the serial flowincremental vapor generating system 218 utilized in the secondembodiment 210 of the power generating system according to the presentinvention comprises a heat exchanger or vaporizer 232 having a primaryloop 234 through which is caused to flow the heating fluid. In theembodiment shown and described herein, the heating fluid comprisesgeothermal brine 216, although other types of heating fluids may beused, as would be obvious to persons having ordinary skill in the artafter having become familiar with the teachings of the presentinvention. The heat exchanger or vaporizer 232 may also comprise firstand second heating sections 236 and 238 arranged so that they are inthermal communication with the primary loop 234 so that heat energycontained in the brine 216 is transferred to the mixed working fluid 214flowing in the first and second heating sections 236 and 238,respectively. The heat exchanger 232 may also be provided with a thirdheating section 240 suitable for additionally heating the combined firstand second vapor portions 220 and 222. For example, and as was the casefor the first embodiment 110, the third heating section 240 of thesecond embodiment 210 is used to heat the first and second vaporportions 220 and 222 above the dew point.

[0072] It is generally preferred that the heat exchanger 232 be of thecounter-current type in which the inlet end of the primary loop 234 isthermally adjacent the “hottest” heating section (e.g., the thirdheating section 240) and the outlet end is thermally adjacent the“coolest” heating section (e.g, the first heating section 236). Such anarrangement allows the system 210 to more closely match the heatingfunction 290 of the working fluid 214 with the cooling function 292 ofthe heating fluid (e.g., brine 216). See FIG. 6.

[0073] The exact number of heating sections (e.g., heating sections 236,238, and 240) comprising the heat exchanger 232 may vary depending onthe particular application, the particular heating and working fluidsused, as well as the number of stages used to achieve the incrementalheating of the working fluid 214 in the serial manner described herein.The number of heating sections comprising the heat exchanger in anygiven application could be readily determined by persons having ordinaryskill in the art after having become familiar with the teachings of thepresent invention and by applying the teachings to the particularapplication. Consequently, the present invention should not be regardedas limited to a heat exchanger having any particular number of heatingsections.

[0074] The heat exchanger 232 may be constructed from any of a widerange of materials and in accordance with any of a wide range oftechniques that are now known in the art or that may be developed in thefuture that would be suitable for the particular application. However,since heat exchangers of the type described herein could be readilyfabricated by persons having ordinary skill in the art after havingbecome familiar with the teachings of the present invention, and sincethe details of such heat exchangers are not necessary to understand orpractice the present invention, the heat exchangers used in theembodiments shown and described herein will not be described in furtherdetail herein.

[0075] The first and second heating sections 236 and 238 of the heatexchanger 232 are operatively associated with an integral separatorsystem 241 comprising a first separator section 242 and a secondseparator section 244. As will be described in greater detail below, thefirst and second separator sections 242 and 244 comprising the integralseparator system 241 separate liquid and vapor portions (not shown) fromrespective first and second heated mixed working fluid streams 219 and221.

[0076] The first separator section 242 of integral separator system 241is provided with an inlet 246 that is connected to the high temperaturerecuperator 256 and the first heating section 236 in the manner bestseen in FIG. 4. The arrangement is such that the first separator section242 receives the first heated working fluid stream 219. The liquidoutlet 250 of the first separator section 242 is connected to an inlet252 of the second heating section 238.

[0077] The second separator section 244 of integral separator system 241is provided with an inlet 260 connected to the outlet 262 of secondheating section 238 so that the second separator section 244 receivesthe second heated working fluid stream 221 from the second heatingsection 238. The second separator section 244 is also provided with acollector 264 for collecting additional amounts of separated liquid. Thecollector 264 is connected to a heating loop 255 of the high temperaturerecuperator 256. A vapor outlet 266 provided in the second separatorsection 244 is connected to the third heating section 240. The outlet270 of the third heating section 240 is connected to the energyconversion system 226.

[0078] The high temperature recuperator 256 is connected to thecollector 264 of the second separator section 244 of integral separator241. The high temperature recuperator 256 recovers heat contained in theliquid portion separated by the second separator section 244 of theintegral separator 241. The recovered heat is used to heat thepre-heated second working fluid stream 282. In the embodiment shown anddescribed herein, the collector 264 is connected to the heating loop 255of the high temperature recuperator 256, whereas a heated loop 257 ofhigh temperature recuperator 256 is connected in parallel with the firstheating section 236 of the heat exchanger 232. The heating loop 255 isconnected to an expansion valve 294 which returns the cooled liquidportion to the low pressure side of the power generating system 210.

[0079] As was the case for the first embodiment 110 (FIG. 1) of thepower generating system, the energy conversion system 226 of the secondembodiment 210 of the power generating system may comprise any of a widerange of systems and devices suitable for converting into useful workheat energy contained in the heated mixed working fluid 214 exiting theseries flow vapor generator 218 (or third heating section 240, if athird heating section is used). By way of example, the energy conversionsystem 226 comprises a turbine 228 and an electric generator 230connected thereto. The turbine 228 and electric generator 230 maycomprise any of a wide range of systems and devices that are well-knownin the art and readily commercially available. Consequently, the turbine228 and electric generator 230 utilized in one preferred embodiment ofthe invention will not be described in greater detail herein.

[0080] The exhaust outlet 272 of turbine 228 is connected to a lowtemperature recuperator 274. The low temperature recuperator 274recovers heat contained in the turbine exhaust stream and uses it topre-heat the mixed working fluid stream 214. More specifically, theexhaust outlet 272 of turbine 228 is connected to a heating loop 273 ofthe low temperature recuperator 274, whereas a heated loop 275 of thelow temperature recuperator 274 is connected between the pump 280 andthe parallel arrangement of the heating loop 257 of the high temperaturerecuperator 256 and the first heating section 236 of heat exchanger 232.The turbine exhaust stream in the heating loop 273 surrenders heat tothe mixed working fluid stream 214 in the heated loop 275, therebypre-heating the mixed working fluid stream 214 before the same entersthe high temperature recuperator 256 and the first heating section 236.Thereafter, the exhaust stream is combined with the separated liquidportion exiting the expansion valve 294. A condenser 276 connected tothe low temperature recuperator 274 and expansion valve 294 receives thecombined cooled mixed working fluid 214, condenses it, and returns it topump 280.

[0081] The condenser 276 may comprise any of a wide range of condensersthat are well-known in the art or that may be developed in the futurethat would be suitable for condensing the combined cooled mixed workingfluid 214. By way of example, in the embodiment shown and describedherein, the condenser 276 comprises an air-cooled condenser in which air296 is used to condense the mixed working fluid 214 flowing in thecondenser 276.

[0082] The second embodiment 210 of the power generation system of thepresent invention may be operated as follows to convert into useful workheat energy derived from the heating fluid, i.e., geothermal brine 216extracted from the earth. As was the case for the first embodiment, thegeothermal brine 216 may enter the primary loop 234 of the heatexchanger 232 at a temperature of about 335° F., although othertemperatures are possible. The mixed working fluid 214 may comprise amixture of ammonia and water and is maintained at a pressure of about250 psia on the high pressure side of the power generating system 210.The low pressure side is maintained at a pressure of about 43 psia.Alternatively, other mixed working fluids may be used at otherpressures, as would be obvious to persons having ordinary skill in theart after having become familiar with the teachings of the presentinvention.

[0083] With reference now to FIGS. 4-6, the mixed working fluid stream214 exits the condenser 276 at station L₀ about the bubble point for themixture 214. This station corresponds to point L₀ in FIG. 5. The pump280 increases the pressure of the mixed working fluid 214 to a pressuresuitable for use in the high pressure side of the power generatingsystem 210. In the embodiment shown and described herein, the highpressure side of the system 210 is maintained at a pressure of about 250psia. Therefore, the pump 280 increases the pressure of the mixedworking fluid 214 to a pressure of about 250 psia. The mixed workingfluid stream 214 exiting the pump 280 is then directed to the heatedloop 275 of the low temperature recuperator 274 which pre-heats themixed working fluid 214. See station 2 of FIG. 4 and corresponding point2 in FIG. 5. The pre-heated mixed working fluid stream 214 is then splitor divided into a first stream 282 and a second stream 284. The firststream 282 is directed through the heated loop 257 of the hightemperature recuperator 256 whereupon it is heated by the liquid portionextracted from the second separator section 244 by the collector 264.The heating characteristics of the high temperature recuperator 256 andthe flow rate of the first stream 282 are such that the first stream 282is heated to a temperature in excess of its bubble point. Thiscorresponds to station 3 ₂ in FIG. 4 and to point 3 ₂ in FIG. 5.

[0084] In the embodiment shown and described herein, the first stream282 is heated to a quality in the range of about 10% to about 40% (30%preferred). This quality range corresponds to a vapor portion range ofabout 80% to about 96% (90% preferred) on a volume basis. So heating thefirst working fluid stream 282 to a vapor portion in the specified rangeprovides for good heat transfer characteristics in the high temperaturerecuperator 256. That is, some loss of efficiency in the hightemperature recuperator 256 will be experienced if the first workingfluid stream 282 is heated to a vapor portion that is substantiallygreater than the vapor portion range described herein. After beingheated in the high temperature recuperator 256, the heated first workingfluid stream 282 mixed with the heated working fluid stream 284 exitingthe first heating section 236 and directed into the inlet 246 of firstseparator section 242 as first heated working fluid stream 219. Seestation 3 in FIG. 4 and corresponding point 3 in FIG. 5.

[0085] The second stream 284 is directed to the first heating section236 of the heat exchanger 232 which heats the second working fluidstream 284 to a temperature in excess of the bubble point. Thiscorresponds to station 3 ₁ in FIG. 4 and to point 3 ₁ in FIG. 5. It isgenerally preferred that the flow rate of the second stream 284 bematched to the heating characteristics of the first heating section 236so that the mixed working fluid 214 comprising the second working fluidstream 284 is heated to about the same quality as the first stream 282.That is, it is preferred that the points 3 ₁ and 3 ₂ in FIG. 5 beapproximately coincident. Stated another way, the second working fluidstream 284 is heated to a quality in the range of about 10% to about 40%(30% preferred), which corresponds to a vapor portion in the range ofabout 80% to about 98% (90% preferred).

[0086] In the embodiment shown and described herein, the mass ratio ofthe first working fluid stream 282 to the second working fluid stream284 is about 1:4. That is, most of the working fluid 214 is directed tothe second stream 284, with only a small amount (i.e., ¼ on a massbasis) being directed through the high temperature recuperator 256 asfirst working fluid stream 282. Of course, the mixed working fluid 214may be divided in accordance with other mass ratios depending on thecharacteristics of the particular system.

[0087] Still referring primarily to FIG. 4, the first separator section242 in integral separator system 241 receives the first and secondheated streams 282 and 284 as combined first heated working fluid stream219 and separates the stream 219 into a liquid portion and a vaporportion 220. The liquid portion exits the liquid outlet 250 of the firstseparator section 242 and is directed to the inlet 252 of the secondheating section 238. The vapor portion 220 is at about the dew point(i.e., 100% quality) for the mixed working fluid 214. This correspondsto station v₁ in FIG. 4 and to point v₁ in FIG. 5.

[0088] The liquid portion from the first separator 242 is at about thebubble point of the mixed working fluid 214. See station 4 in FIG. 4 andpoint 4 in FIG. 5. The liquid portion is directed into the inlet 252 ofthe second heating section 238 whereupon it is heated to a temperaturein excess of the bubble point. This corresponds to station 5 in FIG. 4and to point 5 in FIG. 5. It is generally preferred that the liquidportion be heated to about the same quality as the mixed working fluidat stations 3 ₁ and 3 ₂. That is, the quality of the mixed working fluidstream exiting the second heating section 238 should be about the sameas the qualities of the working fluid streams exiting the first heatingsection 236 and the high temperature recuperator 256. For example, inthe embodiment shown and described herein, the mixed working fluidstream exits the second heating section 238 at a quality in the range ofabout 10% to about 40% (30% preferred). This corresponds to a vaporportion in the range of about 80% to about 98% (90% preferred). Asdiscussed above, heating the mixed working fluid to the quality rangesspecified herein provides a good balance between temperature rise andheat transfer efficiency in the second heating section 238.

[0089] The second separator section 244 of integral separator system 241receives the heated mixed fluid from the second heating section 238 assecond heated mixed working fluid stream 221. The second separatorsection 244 separates the second heated working fluid stream 221 into aliquid portion (not shown) and a vapor portion 222. As mentionedearlier, the first vapor portion 220 from the first separator section242 is used to further separate the vapor portion from the heated mixedworking fluid stream 221. Since, the liquid portion to be separated fromthe second heated mixed working fluid stream is “lean” (e.g., lowerammonia concentration) and since the first vapor portion 220 is “rich”(e.g., higher ammonia concentration), portions of the first vaporportion 220 will condense on the lean liquid portion in the secondseparator section 244. The heat of condensation causes additionalamounts of vapor portion 222 to be produced.

[0090] The liquid portion drained from separator 244 is collected by thecollector 264 and exits the integral separator system 241. Thiscorresponds to station 6 in FIG. 4 and to point 6 in FIG. 5. Thecollected liquid portion then proceeds to the high temperaturerecuperator 256 whereupon it surrenders a portion of its heat to thefirst working fluid stream 282. See station 7 in FIG. 4 andcorresponding point 7 in FIG. 5. Thereafter, the cooled liquid portionis expanded through the expansion valve 294 to the low pressure side ofthe power generating system 210. See station 8 in FIG. 4 and point 8 inFIG. 5. The cooled, expanded liquid portion is then combined with theturbine exhaust stream at station v₆ and corresponding point v₆ in FIG.5.

[0091] The vapor portion 222 produced in the second separator portion244 combines with residual amounts of the first vapor portion 220 fromthe first separator portion 242 and exits the integral vapor separatorsystem 241 as combined vapor stream 286. This corresponds to station v₂in FIG. 4 and to point v₂ in FIG. 5. The combined vapor stream 286 maybe additionally heated by the third heating section 240 to a temperaturethat is greater than the dew point temperature for the combined vaporstream 286. That is, the combined vapor stream 286 is superheated in thethird heating section 240. The superheated stream 288 exiting the thirdheating section 240 corresponds to station v₃ in FIG. 4 and to point v₃in FIG. 5. The stream 288 is then directed to the energy conversionsystem 226.

[0092] As was the case for the first embodiment 110, the energyconversion system 226 of the second embodiment 210 extracts heat energyfrom the superheated stream 288, converting it into useful work. In theembodiment shown and described herein, heat energy contained in thefirst and second vapor streams 220 and 222 (which comprise combinedstream 286 and superheated stream 288) is converted into electrical workby the turbine 228 and the electrical generator 230 comprising theenergy conversion system 226.

[0093] The superheated stream 288 is expanded in the turbine 228 andexits the turbine 228 as exhaust stream 272. See station v₄ in FIG. 4and point v₄ in FIG. 5. It is generally preferred that the expansionprocess be terminated before the mixed working fluid 214 is cooled belowthe dew point temperature. By way of example, in the embodiment shownand described herein, the mixed working fluid 214 is expanded to apressure of about 43 psia and to a temperature of about 160° F., whichis below the dew point of the mixed working fluid 214 at the designatedpressure. The mixed working fluid 214 can be cooled to a temperaturebelow the dew point temperature since the energy conversion device 226can function effectively with wet mixtures. The exhaust stream 272 isthereafter directed to the low temperature recuperator 274 wherein itsurrenders a portion of its heat energy to the working fluid stream 214flowing in the heated loop 275 of low temperature recuperator 274. Thecooled exhaust stream 272 exits the low temperature recuperator 274 atstation v₅ at a temperature between the bubble and dew points for themixed working fluid. See point v₅ in FIG. 5. By way of example, in thisembodiment, the cooled exhaust stream 272 exits the low temperaturerecuperator 274 at a quality in the range of about 0% to about 100% (45%preferred).

[0094] The mixed working fluid exiting the low temperature recuperator274 is then mixed with the liquid portion flowing through the expansionvalve 294. See station v₆ in FIG. 4 and point v₆ in FIG. 5. The combinedworking fluid stream is then condensed by the condenser 276 to about thebubble point (station L₀ in FIG. 4 and point L₀ in FIG. 5). Thecondensed stream is then returned to the high pressure side of thesystem 210 by pump 280 and the cycle is repeated.

[0095] The second embodiment 210 of the power generating system justdescribed results in the closely matched heating and cooling functions290 and 292 shown in FIG. 6. That is, the heating curve 290 of the mixedworking fluid 214 closely follows the cooling curve 292 of the heatingfluid (e.g., geothermal brine 216).

[0096] It is contemplated that the inventive concepts herein describedmay be variously otherwise embodied and it is intended that the appendedclaims be construed to include alternative embodiments of the inventionexcept insofar as limited by the prior art.

1. A power generating system, comprising: a heat source; an incrementalvapor generator system operatively associated with said heat source,said incremental vapor generator system comprising: a first heatingsection, said first heating section receiving a mixed working fluid andgenerating a first heated working fluid stream comprising a vaporportion and a liquid portion; a second heating section operativelyassociated with said first heating section, said second heating sectionreceiving the liquid portion from said first heated working fluidstream, said second heating section generating a second heated workingfluid stream comprising a vapor portion; and an energy conversion deviceoperatively associated with said incremental vapor generator system,said energy conversion device converting into useful work heat energycontained in the vapor portions of the first and second heated workingfluid streams.
 2. The power generating system of claim 1, furthercomprising: a condensing system operatively associated with said energyconversion device, said condensing system receiving an exhaust streamfrom said energy conversion device and condensing the exhaust stream toform a condensed mixed working fluid; and a pump system operativelyassociated with said condensing system and said incremental vaporgenerator system, said pump transferring the condensed mixed workingfluid from said condensing system to said incremental vapor generatorsystem.
 3. The power generating system of claim 1, further comprising afirst separator system having an inlet, a vapor outlet, and a liquidoutlet, the inlet of said first separator system being operativelyassociated with said first heating section, the liquid outlet of saidfirst separator system being operatively associated with said secondheating section, said first separator system separating the vaporportion and the liquid portion of said first heated working fluidstream.
 4. The power generating system of claim 3, further comprising asecond separator system having an inlet, a vapor outlet, and a liquidoutlet, the inlet of said second separator being operatively associatedwith said second heating section.
 5. The power generating system ofclaim 4, further comprising a vapor mixer having a first inlet, a secondinlet, and an outlet, the first inlet of said vapor mixer beingoperatively associated with the vapor outlet of said first separatorsystem, the second inlet of said vapor mixer being operativelyassociated with the vapor outlet of said second separator system, theoutlet of said vapor mixer being operatively associated with said powerconversion system.
 6. Tile power generating system of claim 5, furthercomprising a third heating section operatively associated with said heatsource, the outlet of said vapor mixer, and said energy conversiondevice, said third heating section additionally heating the first andsecond vapor streams.
 7. The power generating system of claim 4, whereinsaid first and second separator systems comprise an integral systemwherein the vapor portion of said first heated working fluid stream fromsaid first separator system at least partially condenses in said secondseparator system the liquid portion from said second heated workingfluid stream.
 8. The power generating system of claim 7 furthercomprising a third heating section operatively associated with said heatsource, said integral first and second separator systems, and saidenergy conversion device, said third heating section additionallyheating the first and second vapor streams.
 9. A method for generatingpower from a mixed working fluid, comprising: incrementally heating themixed working fluid to produce a first vapor stream and a second vaporstream; and converting into useful work heat energy contained in thefirst and second vapor streams.
 10. The method of claim 9, wherein saidstep of incrementally heating comprises: heating the mixed working fluidto produce a first heated working fluid stream comprising a vaporportion and a liquid portion; separating the vapor portion and theliquid portions of the first heated working fluid stream, the separatedvapor portion forming the first vapor stream; and additionally heatingthe liquid portion from the first heated working fluid stream to producethe second vapor stream.
 11. The method of claim 10, further comprisingcombining the first and second vapor streams into a combined vaporstream.
 12. The method of claim 11, further comprising additionallyheating the combined vapor stream to produce a superheated vapor-stream.13. The method of claim 10, further comprising using the vapor portionfrom the first heated working fluid stream to condense on the liquidportion from the second heated working fluid stream and to produceadditional portions of the vapor portion from the first heated workingfluid stream.
 14. The method of claim 13, further comprising combiningthe additional portions of the vapor portion from the first heatedworking fluid stream and the second vapor streams to form a combinedvapor stream.
 15. The method of claim 14, further comprisingadditionally heating the combined vapor stream to produce a superheatedvapor stream.
 16. A power generating system, comprising: a heat source;incremental vapor generating means operatively associated with said heatsource for incrementally generating a first vapor stream and a secondvapor stream from a mixed working fluid; and power conversion meansoperatively associated with said incremental vapor generating means forconverting into useful work heat energy contained in said first andsecond vapor streams.
 17. The power generating system of claim 16,further comprising separator means operatively associated with saidincremental vapor generating means for separating the first and secondvapor streams from a heated working fluid stream from said incrementalvapor generating means.
 18. The power generating system of claim 17,further comprising means for combining said first vapor stream and saidsecond vapor stream to form a combined vapor stream, the combined vaporstream being directed to said power conversion means.
 19. The powergenerating system of claim 17 wherein said separator means comprisesmeans for using a portion of the first vapor stream to condense on aliquid portion from the heated mixed working fluid.
 20. The powergenerating system of claim 16, further comprising: condensing meansoperatively associated with said power conversion means for condensing avapor exhaust from said power conversion means into a condensed mixedworking fluid; and recirculating means operatively associated with saidcondensing means for recirculating condensed mixed working fluid to saidincremental vapor generating means.
 21. An incremental vapor generatorsystem for vaporizing a mixed working fluid, comprising: a first heatingsection operatively associated with a heat source, said first heatingsection receiving the mixed working fluid and generating a first heatedworking fluid stream comprising a vapor portion and a liquid portion; aseparator system operatively associated with said first heating section,said separator system separating the vapor portion and the liquidportion of the first heated working fluid stream; and a second heatingsection operatively associated with the heat source and said separatorsystem, said second heating section receiving the liquid portion fromthe first heated working fluid stream, said second heating sectiongenerating a second heated working fluid stream comprising a vaporportion.